SUPERCONDUCTOR MATERIALS

A. History of SuperconductorsSuperconductors were first discovered by a Dutch physicist , Heike Kamerlingh Onnes , of the University of Leiden in 1911 . On July 10 , 1908, Onnes succeeded in liquefying helium by cooling to 4 K or 269oC . Then in 1911 , Onnes began studying the electrical properties of metals at extremely cold temperatures . At the time it was known that the resistance of a metal will fall when cooled below room temperature , but no one can know how the lower bound constraints is achieved when the metal temperature approaches 0 K or absolute zero . Some scientists at that time as William Kelvin predicted that electrons flowing in the conductor will stop when the temperature reaches absolute zero . On the other hand , others including Onnes scientists estimate that the barriers will disappear in these circumstances . To find out what actually happened, Onnes then drain current in a very pure mercury wire and then measure the resistance while lowering the temperature . At a temperature of 4.2 K , Onnes get resistance suddenly disappeared . The current flowing through the wire mercury constantly.In the absence of obstacles , the current can flow without energy loss . Onnes experiment with a current on a superconducting coil in a closed circuit and then revoke the current source and measure current flow turns one year later still flowing . This phenomenon was named later by Onnes superkondutivitas . The above findings , Onnes was awarded the Nobel Prize in Physics in 1913 .
B. Understanding Superconductors
           Superconductors are materials that have zero electrical resistance at very low temperatures . It means that superconductors can conduct current even in the absence of a voltage source . Characteristics of Superconductors are materials medanmagnet in superconductors is zero and Meissner effect experienced . The resistivity of a material is zero if below its critical temperature .

C. Superconductors group
          Based on the value of the critical temperature , superconducting divided into two groups:

    1 . Low critical temperature superconductors
          This type of superconducting critical temperature less than 23 K. This type of superconducting abandoned because of the cost of expensive to cool the material .

    2 . High critical temperature superconductors
         This type of superconducting critical temperature greater than 78 K. This is a type of superconducting materials are being developed that are expected to obtain the superconducting at room temperature making it more economical .

D. Superconductor applications
           Superconductor applications in life include :a. Power Cord .By using superconducting materials , the electrical energy will not experience dissipation due to resistance in the superconducting material is zero . Then the use of electrical energy will be more efficient .
b . Transport EquipmentThe use of superconductors in the field of transport is super fast Electric Railway , known as the Magnetic Levitation ( Maglev ) .